System of measuring the distribution of reduction rate of metal strips

ABSTRACT

In a system of measuring the distribution of the reduction rate of a metal strip rolled by a rolling mill, a pair of thickness gauges spaced apart with a predetermined spacing and which are reciprocated across the metal strip are provided on the entry and exit sides of the rolling mill and the gauges are controlled such that the same portion of the metal strip is measured on the entry and exit sides of the rolling mill by the pair of thickness gauges.

United States Patent Kubo [ 1 June 20, 1972 [54] SYSTEM OF IWEASURING THE DISTRIBUTION OF REDUCTION RATE OF METAL STRIPS [72] Inventor: Moritada Kubo, Tokyo, Japan [73] Assignee: Tokyo Shibaura Electric Co., Ltd.,

Kawasaki-shi, Japan 221 Filed: Dec. 29, 1970 [21] Appl.No.: 102,356

[30] Foreign Application Priority Data Jan. 7, 1970 Japan ..45/2I14 [52] U.S. Cl. ..73/l59, 250/83, 324/34 TX, 72/16 [51] Int. (I ..B2lb 37/02 [58] Field of Search ..72/6l2, 16; 73/159 [56] References Cited UNITED STATES PATENTS 3,442,104 5/1969 Misaka et a1 .....72/9 3,474,668 10/1969 Mangan ..73/ l 59 Primary ExaminerMilton S. Mehr Attorney-Flynn & Frishauf [57] ABSTRACT In a system of measuring the distribution of the reduction rate of a metal strip rolled by a rolling mill, a pair of thickness gauges spaced apart with a predetennined spacing and which are reciprocated across the metal strip are provided on the entry and exit sides of the rolling mill and the gauges are controlled such that the same portion of the metal strip is measured on the entry and exit sides of the rolling mill by the pair of thickness gauges.

4 Claims, 4 Drawing Figures PME'N'TEDJIIIIEO I972 SHEET 2 BF 2 FIG. 4

I GENERATOR A-D 2 CONVERTER 48 TACHO- AMP DIFFERENTIAL DIFFERENTIAL GENERATOR 3 AMP. AMP.

. 37 I 47 I I6 THICKNESS POTENTIO- GAUGE METER AME MOTOR L 38 43 42 41 I DIFFERENTIAL a. --A 30 AMP COMPARATOR CONVERTER DlVlDER DELA\Y A 0 -40 cIRcuIT 4 AMP coNvERTER N J I 45 T I THICKNESS POTE TIO- ACHO- METER MOTOR GENERATOR I i P e DIFFERENTIAL AD D-A AMP. coNvERTER coNvERTER A-D CONVERTER SYSTEM OF MEASURING THE DISTRIBUTION OF REDUCTION RATE OF METAL STRIPS BACKGROUND OF THE INVENTION This invention relates to a system of measuring the reduction rate of a metal strip before and after rolling by a rolling mill.

It is known in the art that metal strip rolled by a rolling mill tends to bend or warp due to the difference in the reduction rate or elongation rate at various portions of the strip, and that whether the strip is being rolled normally or not can be determined by detecting the configuration of the strip. To detect the configuration of the metal strip it is necessary to detect the transverse distribution of the percentage elongation or the reduction rate of the strip. In one prior approach, a plurality of thickness gauges are juxtaposed in the transverse direction of the strip both on the entry and exit sides of a mill stand and signals derived from the thickness gauges on the entry side are compared with those from the thickness gauges on the exit side.

With this system, however, portions of the metal strip detected by the thickness gauges on the entry side of the mill stand do not accurately correspond to those detected by the thickness gauges on the exit side so that it is difficult to perform accurate control of the rolling operation.

Accordingly, it is an object of this invention to provide a novel system of measuring the transversal distribution of the reduction rate of a metal strip wherein portions measured on the entry and exit sides of a rolling mill coincide accurately.

A further object of this invention is to provide a novel system of measuring the transversal distribution of the reduction rate of a metal strip rolled by a rolling mill by utilizing a pair of thickness gauges positioned on the entry side and on the exit side, respectively, of the rolling mill and are reciprocated across the width of the metal strip. wherein the error caused by the variation in the speed of movement of the thickness gauges at and near the point of reversing the direction of movement of the gauges can be eliminated.

Another object of this invention is to provide a novel control system according to which one of the thickness gauges is caused to precisely follow the movement of the other, thus maintaining the correct spacing between the pair of thickness gauges.

SUMMARY OF THE INVENTION According to this invention there is provided a system of measuring the distribution of the reduction rate of a metal strip rolled by a rolling mill, comprising a first thickness gauge provided on the entry side of the rolling mill, means for moving the thickness gauge across said metal strip, a second thickness gauge provided on the exit side of the rolling mill, the second thickness gauge being spaced apart from the first thickness gauge by predetermined distances both in the transversal direction and longitudinal direction of the metal strip, means for moving the second thickness gauge across the metal strip, means for controlling the relative position of the gauges so that the portion of the metal strip detected by the first thickness gauge coincides with the portion of the metal strip detected by the second thickness gauge on the exit side, and means responsive to the outputs from the first and second thickness gauges to provide a signal representing the reduction rate of the metal plate rolled by the rolling mill.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT With reference first to FIG. 1 of the accompanying drawings a rolling mill stand is designated by a reference numeral 1 by means of which a metal strip 2 is rolled while it is passed through the rolls of the mill in a direction indicated by an arrow at a speed S. A pair of thickness gauges 3 and 4 are disposed to be moved transversely of the strip on the entry and exit sides, respectively of the mill. Thickness gauges 3 and 4 are spaced apart a distance L in the longitudinal direction and a distance P in the transverse direction of the strip.

In FIG. 2, the abscissa X represents the transverse direction of the strip, or the direction of movement of the thickness gauges while the ordinate T represents time. As shown by curves A and B, gauges 3 and 4 are reciprocated in unison across the strip 2 with the definite transversal spacing P. As the speed of gauges 3 and 4 varies at or near the points where their directions of movement are reversed, correct measurement of the thickness can not be assured. Accordingly, in accordance with this invention the stroke of the gauges is made larger than the width C of the strip so as to realize substantially the uniform speed of the gauges 3 and 4 over a distance corresponding to the strip width C.

Assuming now that during a time interval t in which a given point on the metal strip moves the distance L between the gauges on the entry and exit sides at the speed S, the gauge 4 on the exit side is moved at a speed V over the distance P, the gauge of the strip at the given point will at first be detected by gauge 3 and then by gauge 4 on the exit side after elapse of time t, as shown by the following equation.

In a preferred embodiment of this invention diagrammatically illustrated in FIG. 3, thickness gauges 3 and 4 are provided respectively on the entry side and the exit side of a rolling mill. Since the gauge 3 and its associated driving mechanism, position detector and speed detector are identical in construction with gauge 4 and its corresponding driving mechanism and detectors, only the construction of gauge 3 and its associated elements on the entry side are shown and described below for the sake of brevity.

More particularly, the gauge 3 is carried by a carriage 11 driven by a lead screw 14 rotatably joumalled by spaced apart side frames 12 and 13. Lead screw 14 is driven by a reversible motor 16 through a gearing 15 to move carriage 11 along guide rod 17 transversely of the metal strip 2. Thickness gauge 3 comprises an X-ray sensitive means 18 carried by the carriage 11 and a source of X-ray 20 positioned on the opposite side of the strip 2 and carried by a carriage l9. Carriage 19 is also driven by motor 16 through gearings l5 and 21 and a lead screw 22 to be moved along a guide rod 23. Carriages 11 and 19 are moved in unison so that the X-ray sensitive means 18 always confronts the source of X-ray 20. As is well known in the art, the quantity of the X-rays transmitted through the metal strip varies dependent upon the thickness of the strip whereby the member 18 produces an output proportional to the thickness of the metal strip.

A tachometer generator 24 is coupled to gearing 15 to generate an output representing the speed of carriage II and hence thickness gauge 3. Further, the carriage 11 carries a sliding arm 26 co-operating with a resistance wire 25 extending between side frames 12 and 13. Thus, the potentiometer 27 comprised by resistance wire 25 and sliding arm 26 produces an output representing the position of thickness gauge 3. Another tachometer generator 28 is secured to side frame 28 with its driving roller 29 contacted with the surface of strip 2 to generate an output proportional to the running speed thereof.

As above described, another thickness gauge 4 of the identical construction is provided on the exit side of the mill stand.

FIG. 4 shows a block diagram of a control circuit embodying the invention. The output from the thickness gauge 3 provided on the entry side of the rolling mill 1 (FIG. 1) is applied to one input terminal of a differential amplifier 31 through a delay circuit 30 having a delay time 1 corresponding to the above-mentioned time interval. t. A portion of the output of the thickness gauge is also applied to an analogue-digital converter 32 to be converted into a digital signal. The other input terminal of the differential amplifier 31 receives the output from thickness gauge 4 on the exit side of the mill stand. Accordingly, the differential amplifier 31 provides an output corresponding to the difference in the gauge of a given point of the strip before and after reduction. This output is also converted into a digital signal by another analogue-digital converter 33, and the output from both analogue-digital converters 32 and 33 are applied to a divider 34 to obtain a signal representing the ratio between the reduction in the skip gauge efl'ected by the rolling operation and the strip gauge before rolling, that is the reduction rate. If desired, the digital signal representing the reduction rate is converted into an analogue signal through a digital-analogue converter 35 and is applied to an output terminal 36 to be used as the control signal for the mill stand. Since thickness gauges 3 and 4 are reciprocated across the surface of the running strip 2, a distribution of the reduction rate is obtained along a line inclined to the longitudinal axis of the strip.

In the above described equation I P/ V= US where various values P, V, L and S do not vary, output terminal 36 provides a signal representing the desired reduction rate distribution. Actually, however, as thickness gauges 3 and 4 are reciprocated, their speeds vary substantially at and near the points at which their directions of movement are reversed. in addition, the running speed S of the strip often varies depending upon the load of the rolling mill. Accordingly, the circuit illustrated is designed by taking into consideration of thesevariations.

Positional signals of gauges 3- and 4 provided by potentiometers 27 and 37 are applied to a difierential amplifier 38 to produce a signal representing the actual distance between two gauges.

The desired set value P of the distance between gauges 3 and 4 can be provided by comparing a signal representing the speed of gauge 3 which is obtained from tachometer generator 24 through an analogue-digital converter 39 with a signal representing the running speed of the metal strip 2 which is obtained from tachometer generator 28 through an analoguedigital converter 40, by means of a divider 41. The output from divider 41 representing the set value P is converted into an analogue signal through a digital-analogue converter 42 and the analogue signal is applied to a comparator 43 together with the signal from differential amplifier 38 representing the actual distance. Where the actual distance between gauges 3 and 4 equals the set value P, comparator 43 will produce no output whereas when the actual distance is not equal to the set value P, a signal will be applied to a correction motor 45 (not shown in FIG. 3 but coupled to gauge 4) through a variable gain amplifier 44, which is provided when derired, to correct the position of the gauge 4 to correct the actual distance between gauges to the set value P. In this manner, gauges 3 and 4 are controlled to always maintain the set value P of the spacing.

Where an independent driving mechanism is not provided for gauge 4, motor 45 is operated to control gauge 4 to follow the movement of gauge 3. More particularly the output from tachometer generator 24 and that of potentiometer 27 are applied to a differential amplifier 48 respectively through variable amplifiers 46 and 47. To move gauge 3 along semisolid curve A, FIG. 2, there is provided a signal generator 49 which produces a triangular wave signal. The output from generator 49 is applied to a differential amplifier 50 together with the output from difl'erential amplifier 48 thus producing a differential signal between the output from signal generator 49 representing the target or desired position of the gauge 3 and the output from potentiometer 27 representing the actual position of the gauge 3. The output, if any, from varies the number of revolutions of motor 16 so that e gauge 3 is moved correctly along curve A. The output from potentiometer 27 is not directly applied to differential amplifier 50 but instead through differential amplifier 48 wherein the output from tachometer generator 24 is subtracted. It is to be understood that the differential amplifier 48 is used as a type of a bufier circuit for preventing motor 16 from being directly infiuenced by the output from potentiometer 27 by taking into consideration the rotational inertia of motor 16.

In this embodiment, where the speed of the gauges is made sufiiciently higher than the running speed S of the metal strip, it is possible to detect the reduction rate distribution substantially in the transverse direction of the strip.

What is claimed is:

l. A system of measuring the distribution of the reduction rate of a metal strip rolled by a rolling mill comprising a first thickness gauge provided on the entry side of said rolling mill, means for moving said thickness gauge across said metal strip, a second thickness gauge provided on the exit side of said rolling mill, said second thickness gauge being spaced apart from said first thickness gauge by predetermined distances both in the transverse direction and longitudinal direction of said metal strip, means for moving said second thickness gauge across said metal strip, means for controlling the relative position of said gauges so that the portion of said metal strip detected by said first thickness gauge coincides with the portion of said metal strip'detected by said second thickness gauge on the exit side, and means responsive to the outputs from said first and second thickness gauges to provide a signal representing the reduction rate of said metal strip rolled by said rolling mill.

2. The system according to claim 1 wherein said gauge position control means comprises means for reciprocating said first and second thickness gauges at predetermined speed across said metal strip while maintaining a predetermined spacing between said thickness gauges.

3. The system according to claim 1 wherein said position control means comprises first and second potentiometers for detecting the positions of said first and second thickness gauges,.respectively, a first differential amplifier for detecting the difference between the outputs from said first and second potentiometers, first and second tachometer generators respectively detecting the travelling speed of said first thickness gauge and the running speed of said metal strip, a first divider for producing a signal representing a set distance between said first and second gauges represented by the ratio between outputsof said first and second tachometer generators, a comparator for comparing the output from said first divider with the output from said first differential amplifier, a signal. generator for generating a signal of a triangular waveform representing the loci of the reciprocating movements of said first and second gauges, a second difi'erential amplifier for producing a signal corresponding to the difference between the output from said signal generator and the output from said first potentiometer, and means responsive to the output from said second differential amplifier to control the position of said first thickness gauge.

4. The system according to claim 1 which further includes means for comparing the position of said second thickness gauge with the position of said first thickness gauge for correcting the position of said second thickness gauge with respect to the position of the first thickness gauge so as to maintain the spacing between said two thickness gauges at a predetermined spacing.

amtpllifier 50 a 

1. A system of measuring the distribution of the reduction rate of a metal strip rolled by a rolling mill comprising a first thickness gauge provided on the entry side of said rolling mill, means for moving said thickness gauge across said metal strip, a second thickness gauge provided on the exit side of said rolling mill, said second thickness gauge being spaced apart from said first thickness gauge by predetermined distances both in the transverse direction and longitudinal direction of said metal strip, means for moving said second thickness gauge across said metal strip, means for controlling the relative position of said gauges so that the portion of said metal strip detected by said first thickness gauge coincides with the portion of said metal strip detected by said second thickness gauge on the exit side, and means responsive to the outputs from said first and second thickness gauges to provide a signal representing the reduction rate of said metal strip rolled by said rolling mill.
 2. The system according to claim 1 wherein said gauge position control means comprises means for reciprocating said first and second thickness gauges at predetermined speed across said metal strip while maintaining a predetermined spacing between said thickness gauges.
 3. The system according to claim 1 wherein said position control means comprises first and second potentiometers for detecting the positions of said first and second thickness gauges, respectively, a first differential amplifier for detecting the difference between the outputs from said first and second potentiometers, first and second tachometer generators respectively detecting the travelling speed of said first thickness gauge and the running speed of said metal strip, a first divider for producing a signal representing a set distance between said first and second gauges represented by the ratio between outputs of said first and second tachometer generators, a comparator foR comparing the output from said first divider with the output from said first differential amplifier, a signal generator for generating a signal of a triangular waveform representing the loci of the reciprocating movements of said first and second gauges, a second differential amplifier for producing a signal corresponding to the difference between the output from said signal generator and the output from said first potentiometer, and means responsive to the output from said second differential amplifier to control the position of said first thickness gauge.
 4. The system according to claim 1 which further includes means for comparing the position of said second thickness gauge with the position of said first thickness gauge for correcting the position of said second thickness gauge with respect to the position of the first thickness gauge so as to maintain the spacing between said two thickness gauges at a predetermined spacing. 